We can classify the usages of IP addresses into 3 categories
- Unicast
- Broadcast
- Multicast

TCP is connection-oriented protocol(= one host IP to another host IP ), therefore broadcasts or multicasts do not apply to TCP
Broadcasts or multicasts only applies to UDP

ARP & RARP also use broadcasts
What is the difference?
The difference exists due to the layer a protocol operates on.

Example---Unicasting
At IP layer---Sending a message only to one IP address
At MAC layer -->Sending a message only to only one NIC

Packet filtering on a received message
When a frame/packet is received, several layers of filtering occurs:

(1) NIC(Network Interface Card) filtering

-NIC sees every frame and filters and passes only error-free frames addressed to it or multicasted or broadcased frames

- A NIC can be forced into a "promiscuous mode" to receive all frames on the net-->Network Analyzers(e.g. Sniffer) work in this mode to capture all packets and analyze them for trouble shooting a network.

- Most NICs can also be configured to receive multicast or broadcast

- On Ethernet, the IP layer's multicast is recognized by hardware address 01:00:5e:00:00:00 through 01:00:5e:7f:ff:ff

- Ethernet broadcast address is ff:ff:ff:ff:ff:ff -- Where are the Ethernet broadcasts used?

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*** Ethernet Broadcast Addresses Updated 12/2/98 ***
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Ethernet Type
Address Field Usage
------------------ ----- -------------------------------------------------
FF-FF-FF-FF-FF-FF 0806 ARP (for IP and CHAOS) as needed
FF-FF-FF-FF-FF-FF 1600 VALID packets, Hello or gateway search?
1 packets every 30 seconds, per VALID station
FF-FF-FF-FF-FF-FF 8035 Reverse ARP
FF-FF-FF-FF-FF-FF 809B EtherTalk

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*** Ethernet Multicast Addresses Updated 12/2/98 ***
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Ethernet Type
Address Field Usage
------------------ ----- -------------------------------------------------
01-00-0C-DD-DD-DD ???? CGMP (Cisco Group Management Protocol)
01-00-1D-00-00-00 -802- Cabletron PC-OV PC discover (on demand)
01-00-5E-00-00-00 0800 DoD Internet Multicast (RFC-1112)
01-80-C2-00-00-00 -802- Spanning tree (for bridges)
01-80-C2-00-00-0F
01-80-C2-00-00-10 -802- Bridge Management
03-00-00-00-00-01 -802- NETBIOS
03-00-00-00-80-00 -802- Bridge
09-00-07-00-00-00 -802- AppleTalk Zone multicast addresses
through
09-00-07-00-00-FC
09-00-07-FF-FF-FF -802- AppleTalk broadcast address
33-33-00-00-00-00 86DD IPv6 Neighbor Discovery
through
CF-00-00-00-00-00 9000 Ethernet Configuration Test protocol (Loopback)

(2) Device Driver filtering
- The frame type must belong to a protocol that is supported(IP, ARP, RARP) by this station

- Multicast filtering--Do I belong to the multicast group? If an application registered to a multicast group then the station remembers the mutlicast group address

(3) IP Layer filtering
- Filters based on source & destination address(unicast or multicast) and also based on Protocol field(ICMP, UDP, TCP, …)

- Passes to a higher layer(TCP or UDP, …)

(4) UDP/TCP filtering
- Filters based on Destination port number--if no process is currently attached to the number, then generate ICMP port unreachable message

- Also checks TCP/UDP header checksum--if error, then "silently discard" the packet

Broadcasting
- 4 kinds
Limited,
Net-directed,
Subnet-directed,
All-subnets-directed